In competitive inhibition, Km increases while Vmax remains unchanged.

Explanation

### Step-by-Step Solution:

1. **Understanding Competitive Inhibition**:
- Competitive inhibition occurs when an inhibitor competes with the substrate for binding to the active site of an enzyme. The inhibitor is often structurally similar to the substrate, allowing it to bind to the active site.

2. **Effect on Km**:
- Km (Michaelis constant) is a measure of the substrate concentration required to reach half of Vmax. In competitive inhibition, as the concentration of the inhibitor increases, more substrate is required to outcompete the inhibitor for binding to the active site. This results in an increase in Km, indicating that a higher concentration of substrate is needed to achieve the same reaction rate.

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